Help with resistor

[speedman]

Hi all, newbie here. I am not an electronic engineer, etc... but like to do some basic stuff myself.
I have a problem with a car loom. One of the resistors in my loom blew.

There is nothing written on it, so I need to know how I can find out it's resistance and Wattage. The only thing I know is that it has a 12V supply (being a car loom). How can I know the rest? From pics and sizes of other similar resistors, it looks like it is a 25W 4.7Ohm resistor. How can I know for sure?

Thanks in advance to all

 

[speedman]

The resistor is this:

It is just above 1 inch in length.

Thanks

 

[praveesh]

The resistor is this:
It is just above 1 inch in length.

Thanks

resistance of a resistor can be found out if there is colour coding above it. Means if there is a colour pattern above the resistor please not it. Each colour gives a specified value.
Black -0 brown 1 red 2 orange 3 yellow 4 green 5 blue 6 violet 7 grey 8 white 9
first colour band gives the first digit of resistance value . Second colour indicates the second digit . Third colour usually gives multiplayer ( only for 4 colour system . For 5 colour it gives the third digit and fourth colour gives the multiplayer). Multiplayer is 10 raised to the given value. 4th colour gives precision(not so important in case of yours . Usually the colours used are gold 5% silver 10% and no colour 20% ).
Eg : red black brown gold
20x(10) (+or -) 5%
means resistance value lies between 210 ohms and 190 ohms
after finding the resistance, find the power by the following equation . Power= voltage x voltage /resistance .
Buy a resistor with power rating higher than the power calculated .
It's better taking the old resistor with you while you go to shop.

From the size of the resistor you have told, the power rating is about 2w

Best wishes

 

[Resqueline]

With it being blown and nothing written on it there's no telling from the resistor itself what resistance it had. These 25W resistors can be had from 0.005 to 36000 ohms, with a common/standard range of 0.1 to 15000 ohms. How did you figure 4.7 ohms?
You'll most likely have to resort to detective work.:
1: Do you see any remains of the resistance wire inside? If so, can you estimate the total length wound up inside?
2: Was it bolted to anything? (These can only dissipate 12.5W in free air, much less if hidden in a loom.)
3: Do you know what circuit/device it was connected to?
4: What car make & model is it from? (Search for a wiring diagram.)

praveesh: you are correct with regards to color coded carbon film (old) resistors, but from the picture you should be able to tell that this is something completely different.